Attentuating adaptor for an inductive shrinkage appliance

ABSTRACT

An attenuating adaptor is proposed in the form of a sleeve ( 23 ) which is composed of non-ferromagnetic metal for insertion radially during operation between a holding section ( 11 ) (which is provided with a central holding opening ( 15 ) for holding a tool shank with a press fit) of a tool holder ( 1 ) and an induction coil arrangement ( 19 ) (which concentrically surrounds the holding section ( 11 ) in order to widen it thermally) of a shrinkage appliance ( 5 ) which feeds alternating current to the induction coil arrangement ( 19 ). The sleeve ( 23 ) can be provided with slots which pass through its wall and whose number, axial length and circumferential width influence the attenuating characteristics of the sleeve ( 23 ). Sleeves ( 23 ) of different sizes are provided for a set of different tool holders ( 1 ), and their attenuating characteristics are chosen such that all of the tool holders ( 1 ) in this set can be shrunk using one and the same setting of the shrinkage appliance ( 5 ).

The invention relates to an attenuating adaptor for an inductiveshrinkage appliance, and to a set of such attenuating adaptors.

From WO 01/89758 A1, it is known for rotating tools, for example drillsor milling cutters or the like, to be shrunk by means of a shrinkageappliance into a central holding opening in a tool holder. The holdingopening is provided in a holding section (which is in the form of asleeve) of the tool holder and has a nominal diameter which is somewhatsmaller than the diameter of the tool shank to be inserted into theholding opening. The holding section can be thermally widened by meansof an induction coil arrangement which concentrically surrounds theholding section during operation, so that the tool shank can be insertedinto the holding opening, and can be removed from it again. Aftercooling down, the holding section holds the tool shank shrunk in in arotationally fixed manner, with a press fit.

The shrinkage appliance feeds high-frequency alternating current orpulsed direct current to the induction coil arrangement, with thecurrent level and/or the frequency and/or the time for which it isapplied being preset by a controller in order on the one hand to ensureadequate heating of the holding section, but on the other hand toprevent undesirable overheating.

This power supply data must normally be set on the shrinkage applianceas a function of the type of tool holder to be heated. Where it isintended to insert and remove tool shanks with diameters of differentsize, the parameters to be set on the shrinkage appliance arecomparatively non-critical, so that tool holders from a predeterminedsize range can also be thermally widened using one and the same setting.In contrast, tool holders with a relatively thin-walled holding sectionare critical, such as those which are intended, in particular, forclamping tool shanks with a diameter of only a few millimeters, forexample three to six millimeters. The energy setting parameters for theshrinkage appliance must be complied with exactly for tool holders suchas these with a thin-walled holding section. Furthermore, with toolholders such as these, their size dimensions differ only slightly sothat the type designations applied to the tool holders must be observedexactly. This makes shrinkage operation more difficult, particularlywhen tool holders of different size are intended to be shrunksuccessively.

One object of the invention is to indicate a way to allow the risk ofoverheating of sensitive tool holders, in particular of tool holderswith a thin-walled holding section, to be reduced.

In order to achieve this object, an attenuating adaptor is proposed inthe form of a sleeve which is composed of non-ferromagnetic metal forloose insertion radially during operation between a holding section(which is provided with a central holding opening for holding a toolshank with a press fit) of a tool holder and an induction coilarrangement (which concentrically surrounds the holding section in orderto widen it thermally) of a shrinkage appliance which feeds alternatingcurrent to the induction coil arrangement.

Normally, the power of the shrinkage appliance is designed to besufficiently great that it is able to sufficiently quickly inductivelyheat tool holders for tool shanks with diameters of up to several 10s ofmillimeters, for example up to 50 millimeters, in order not only toclamp the tool shank but also to allow it to be removed from the toolholder again. It has been found that, with a sleeve which is composed ofnon-ferromagnetic metal and is thus magnetically impermeable, themagnetic flux in the holding section, which is normally composed offerromagnetic material, such as steel, of the tool holder can beattenuated sufficiently to make it possible to avoid undesirableoverheating of the holding section, even if the energy parameters of theshrinkage appliance have not been adapted exactly. Since the sleeve iscomposed of metal, eddy currents are induced in it which weaken themagnetic flux in the holding section. The sleeve is preferably in thiscase located with its inner circumferential surface at least on asubarea of its axial length in flat touching contact with the outercircumferential surface of the holding section, so that, to a certainextent, it dissipates the heat from the holding section. It has beenfound that the eddy current heating of the sleeve is less than the eddycurrent heating of the ferromagnetic holding section, which carries themajority of the magnetic flux, of the tool holder. The innercircumferential casing of the sleeve is expediently conical,corresponding to the shape of the holding section, which is normallylikewise conical, at least in the area of the flat touching contact.

In order to make it possible to fit the sleeve reproducibly in the sameposition on the holding section of the tool holder, the sleevepreferably has a stop which projects radially inwards at its axial endadjacent to the insertion side of the tool shank, by means of which stopthe sleeve can be positioned axially on one end surface of the holdingsection. Not least, the induction coil arrangement can then itself beaxially positioned with a similar axial stop on the sleeve which hasbeen axially positioned in this way, in order to achieve reproducibleinduction conditions.

The sleeve is expediently composed of copper, aluminum or of an alloy ofone of these metals, in order to achieve adequate thermal conductivitycharacteristics.

The attenuating characteristics of the sleeve may vary in many ways. Onthe one hand, the wall thickness of the sleeve may be varied. However,the sleeve preferably has at least one slot which passes radiallythrough the sleeve and extends essentially axially over at least a partof the axial length of the sleeve. The slot opens the wall of the sleevefor the magnetic flux, so that the attenuation of the magnetic flux canbe controlled over the axial length of the slot and of its width in thecircumferential direction. The length and width of the slot furthermorelimits the contact area in which the sleeve makes a touching contactwith the holding section of the tool holder, and thus the coolinginfluence which the sleeve has on the holding section.

In order to allow the contact area (which transmits heat) between thesleeve and the holding section to be varied even better, the sleeve ispreferably provided with an annular cutout in at least one axialsubsection on its inner circumferential surface. Since the sleeve isslotted, it has radially elastic characteristics and can thereforebetter match the circumference of the holding section, thus improvingthe heat transmission characteristics.

In order to distribute the attenuation characteristics of the sleeveuniformly over the circumference of the holding section, the sleevepreferably has two or more slots arranged distributed at equal angularintervals in the circumferential direction. The slots are preferablyarranged diametrically opposite in pairs in the circumferentialdirection, in particular in such a way that the slots pass through thesleeve alternately in the circumferential direction starting fromaxially opposite ends of the sleeve, over a part of its axial length.Slots such as these produce a sleeve with a meandering circumferentialstructure, which can be matched particularly well to the externalcircumference of the holding section.

In order to allow the holding section of the tool holder to be cooleddown again as quickly as possible after being thermally heated, it isknown for a cooling collar to be fitted to the holding section. Thecooling collar may be a simple, air-cooled heat sink with cooling ribs.However, as is known in detail from WO 01/89758 A1, the cooling collarmay also be connected to a liquid cooling circuit. In one preferredrefinement, the outer circumferential surface of the sleeve is conicaland thus allows the cooling collar to be fitted.

A second aspect of the invention relates to an adaptor set which has twoor more of the attenuating adaptors as explained above and is associatedwith a set of different tool holders. The sleeves for an adaptor setsuch as this are designed with the holding section having externalcontours which differ from one another, and/or with the holding openingshaving different internal diameters from one another for fitting ontothe holding section of tool holders, and such that the holding sectionsof the tool holders (which are provided with the associated sleeves) canbe thermally widened with the same alternating current feed setting ofthe shrinkage appliance in each case. All of the tool holders associatedwith the set can be thermally widened using one and the same energyparameter setting of the shrinkage appliance, since the attenuating andcooling characteristics of the sleeves are designed such that themagnetic flux in the holding section complies with the predeterminedlimits for the individual tool holders. For this purpose, the wallthicknesses of the sleeves and/or the number of the slots and/or theaxial lengths of the slots and/or the widths of the slots in thecircumferential direction of the sleeve and/or the dimensions of theannular cutouts which are provided in the inner circumferential surfacesof the sleeves are chosen such that the holding sections of the toolholders (which are provided with the associated sleeves) can bethermally widened adequately, but without any overheating. The dimensionparameters explained above can in this case be determined empirically bya small number of trials.

In this case, all of the sleeves in the set expediently have outercircumferential surfaces with the same contour and with the samediameter, so that one and the same cooling collar can also be used forcooling the thermally widened tool holders.

The invention will be explained in more detail in the following textwith reference to a drawing, in which:

FIG. 1 shows a tool holder of the shrinkage type, with an attenuatingadaptor fitted in a shrinkage appliance;

FIG. 2 shows the tool holder with the attenuating adaptor fitted, andwith a cooling collar an attenuating adaptor fitted, and with a coolingcollar fitted;

FIG. 3 shows an axial longitudinal section through an attenuatingadaptor, seen along a line III-III in FIG. 4, and

FIG. 4 shows a plan view of the attenuating adaptor, seen in thedirection of an arrow IV in FIG. 3.

FIG. 1 shows a tool holder 1 with an attenuating adaptor 3, which isassociated with it and will be explained in more detail in the followingtext, in a shrinkage operating position of a shrinkage appliance, whichis generally annotated 5. A shrinkage appliance such as this isdescribed in detail, for example, in WO 01/89758 A1.

The tool holder 1 has a standardized coupling section 7 by means ofwhich it can be coupled in a rotationally fixed and axially positionedmanner to the rotating spindle of a machine tool and, centrally withrespect to its axis of rotation 9, has a holding section 11 which is inthe form of a sleeve and has a conical, outer circumferential surface 13and a central holding opening 15, whose diameter in a clamping area 17,which is intended for holding the shank of a rotating tool (which is notillustrated in any more detail), for example of a drill or of a millingcutter, is somewhat smaller than the diameter of the tool shank.

The holding section 11 of the tool holder 1 is composed of ferromagneticmaterial, for example heat-resistant steel, so that it concentrates themagnetic flux from an induction coil arrangement 19, which coaxiallysurrounds the holding section 11 for shrinkage operation, when theinduction coil arrangement 19 is fed with a high-frequency alternatingcurrent at a selectable level from an AC generator 21. The magnetic fluxinduces eddy currents in the holding section 11, which heat the holdingsection 11 and thus thermally widen the holding opening 15 to aninternal diameter which is larger than the diameter of the tool shank.The tool shank can be inserted into the widened holding opening 15, orcan be removed from it. Once the holding section 11 has cooled down, thetool shank which has been inserted into the holding opening 15 is heldfirmly, with a press fit.

The level of the alternating current which is produced by the generator21, the time interval in which the alternating current is fed to theinduction coil arrangement 19, and, if appropriate, the frequency of thealternating current determine the amount of induction energy supplied tothe holding section 11, and thus the rate at which the holding section11 is widened, as well as the temperature of the holding section 11 andthus the widened diameter of the holding opening 15 that is achieved.Particularly in the case of a thin-walled holding section 11, as isshown in FIG. 1, the above parameters must be complied with exactly inorder on the one hand to widen the holding opening 15 sufficiently, andon the other hand to avoid overheating of the holding section 11, whichcan lead to destruction of the tool holder 1. In the case ofconventional shrinkage appliances, the parameters must therefore beindividually matched to the respective type of tool holder 1, to beprecise even for tool holders whose holding section and holding openingdimensions differ only slightly. Particularly when different toolholders from a set of similar tool holders are intended to be shrunksuccessively, the setting of the shrinkage appliance requires increasedcare. In order to simplify operation of the shrinkage appliance in asituation such as this, each of the tool holders 1 in the set has aseparate associated attenuating adaptor 3, according to the invention,whose attenuating characteristics are designed in the manner which willbe explained in more detail in the following text, such that all of thetool holders 1 in the set can be inductively heated using one and thesame energy setting for the shrinkage appliance 5, when using therespectively associated attenuating adaptor 3. The attenuating adaptor 3adjusts the magnetic flux that acts on the holding section 11 such that,on the one hand, the holding opening 15 is sufficiently widened and, onthe other hand, overheating of the holding section 11 is avoided.

The attenuating adaptor 3 is generally in the form of a sleeve 23, andis composed of a non-ferromagnetic metal, that is to say a magneticallyimpermeable metal, such as copper or preferably aluminum or an alloy ofone of these metals. As can be seen best in FIGS. 3 and 4, the innercircumferential surface 25 of the sleeve 23 has a conical shape, whichis matched to the conical surface 13 of the holding section 11 for aflat touching contact. Adjacent to the tool insertion end of the holdingsection 11, the sleeve 23 has, at its corresponding axial end, stop tabs27, which project radially inwards, axially position the sleeve 23 atthe axial end of the holding section 11, and ensure a defined positionof the sleeve 23 relative to the holding section 11. The end 29 which isadjacent to the stop tabs 27, as shown schematically in FIG. 1, allowsthe axial position of the induction coil arrangement 19 relative to theholding section 11 via a stop 31 on the coil side.

The circumferential wall of the sleeve 23 has two or more slots 33, inthis case eight slots 33, which are distributed uniformly in thecircumferential direction and pass radially through the sleeve 23, butwhich extend in the axial direction only over a subsection of the axiallength of the sleeve 23. In the illustrated exemplary embodiment, theslots 33 are each diametrically opposite one another in pairs, withslots 33 which are adjacent in the circumferential direction eachoriginating from different axial end surfaces of the sleeve 23, butwhich do not reach the respective other end surface. Thus, overall, thesleeve 23 has a meandering, radially elastic wall structure, whichallows it to be elastically matched to the area of the outercircumferential surface 13 of the holding section 11.

The attenuating behavior of the attenuating adaptor 3 is governed by thewall thickness of the sleeve 23, by the number, the axial length and thewidth of the slots 33 in the circumferential direction and, ifappropriate, by annular cutouts in the inner circumferential surface 25,as are indicated in the area of the axial ends of the sleeve 23, at 35,in FIG. 3. The attenuating adapters 3 which are associated with theindividual tool holders 1 in the set can be designed by suitable choiceof these dimension parameters such that the shrinkage process can becarried out for all of the tool holders 1 in the set using one and thesame setting for the parameters which govern the energy for theshrinkage appliance 5.

All of the attenuating adaptors 3 in the set have a conical outercircumferential surface 37 with the same dimensions and the same coneangle within the set, so that one and the same cooling collar 39 can befitted as standard to the attenuating adaptor, which is still seated onthe holding section 11 from the shrinkage process, for all of the toolholders 1 in the set, for cooling of the thermally widened tool holder 1(FIG. 2). In the illustrated exemplary embodiment, the cooling collar 39is in the form of a collar which can be connected to a liquid circuit,as is explained in detail in WO 01/89758 A1. Air-cooled heat sinks canlikewise be used.

1. An inductive shrinkage appliance comprising: a tool holder having aholding section with a central holding opening configured to hold a toolshank with a press fit; an induction coil arrangement concentricallysurrounding the holding section; and an attenuating adaptor configuredfor insertion between the holding section of the tool holder and theinduction coil arrangement, wherein the attenuating adaptor is in theform of a sleeve composed of non-ferromagnetic metal; wherein theinduction coil arrangement is configured to provide a magnetic fluxbetween the induction coil arrangement and the tool holder through theattenuating adaptor to thermally widen the central holding opening ofthe tool holder; wherein the attenuating adaptor is configured to bepositioned within the inductive shrinkage appliance so that an innercircumferential surface of the attenuating adaptor is brought intocontact with an outer circumferential surface of the holding section ofthe tool holder, with at least a portion of the inner circumferentialsurface of the attenuating adaptor being in flat touching contact withthe outer circumferential surface of the holding section; wherein theinner circumferential surface of the attenuating adaptor includes aconical portion configured to contact at least the outer circumferentialsurface of the holding section; wherein the attenuating adaptor includesa plurality of slots passing radially through the attenuating adaptoralternately in the circumferential direction, starting from axiallyopposite ends of the attenuating adaptor, over at least a part of theaxial length of the attenuating adaptor; wherein the attenuating adaptorincludes a stop tab projecting radially inward at its axial end adjacentto an insertion side for the tool shank, wherein the stop is configuredto position the attenuating adaptor axially at one end surface of theholding section; and wherein the induction coil arrangement comprises astop adapted to axially position the induction coil arrangement withrespect to an end surface of the attenuating adaptor.
 2. The inductiveshrinkage appliance of claim 1, wherein the attenuating adaptor includesa plurality of slots arranged diametrically opposite in pairs in thecircumferential direction.
 3. The inductive shrinkage appliance of claim1, further comprising an annular cutout in at least one axial subsectionof the inner circumferential surface of the attenuating adaptor.
 4. Theinductive shrinkage appliance of claim 1, wherein the attenuatingadaptor is composed of a metal selected from the group consisting ofcopper, aluminum, and any combination thereof.
 5. The inductiveshrinkage appliance of claim 1, wherein the attenuating adaptor has anouter circumferential surface that is conical and that is configured tofit into a cooling collar.
 6. An inductive shrinkage appliancecomprising: a plurality of tool holders, each having a holding sectionwith a central holding opening configured to hold a tool shank with apress fit; wherein the configuration of each of the plurality of toolholders is different from one another; an induction coil arrangementconfigured to concentrically surround the holding section of one of theplurality of tool holders when placed in an inductive shrinkageappliance; a plurality of attenuating adaptors, each attenuating adaptorbeing configured to be removably inserted between one of the pluralityof tool holders and the induction coil arrangement; wherein theinduction coil arrangement is configured to provide a magnetic fluxbetween the induction coil arrangement and any one of the plurality oftool holders through the corresponding attenuating adaptor to thermallywiden the central holding opening of the tool holder, wherein theinduction coil arrangement is configured to accomplish the thermalwidening using the same energy setting for each one of the plurality oftool holders; and wherein the attenuating adaptor includes a stop tabprojecting radially inward at its axial end adjacent to an insertionside for the tool shank, wherein the stop tab is configured to positionthe attenuating adaptor axially at one end surface of the holdingsection.
 7. The inductive shrinkage appliance of claim 6, wherein eachof the plurality of attenuating adaptors has at least one of an externalcontour, an internal diameter of the holding opening, a wall thickness,number of slots, axial length of slots, widths of slots, and dimensionof an annular cutout that differs from each of the other attenuatingadaptors.
 8. The inductive shrinkage appliance of claim 6, wherein eachof the plurality of attenuating adaptors has an outer circumferentialsurface with the same contour and the same diameter as each of the otherattenuating adaptors.
 9. The inductive shrinkage appliance of claim 6,wherein the energy setting includes a level of alternating currentdelivered to the induction coil arrangement, the time interval at whichthe alternating current is fed to the induction coil arrangement, andthe frequency of the alternating current.